1. Field the Invention
The present invention relates to an active distance measuring apparatus which projects modulated light to an object and measures a distance based on reflected light.
2. Related Background Art
As an active distance measurement apparatus of this type, an apparatus which pulse-modulates an infrared ray and projects it to an object has been known (for example, see U.S. Pat. No. 4,758,082 and U.S. Pat. No. 5,008,695). As a photo-sensor thereof, a photo-position sensing device (PSD) which takes out photo-currents I.sub.1 and I.sub.2 from a pair of output electrodes in accordance with an incident position of the reflected light has been known.
In such a distance measuring apparatus, the photo-currents I.sub.1 and I.sub.2 which are alternating current signals having a frequency equal to that of pulse-modulated light are periodically switched and they are converted to photo-signals S.sub.1 and S.sub.2 by current-voltage conversion amplifiers. The signals S.sub.1 and S.sub.2 are further amplified to appropriate voltages V.sub.S1 and V.sub.S2 by amplifiers. Then, the voltages V.sub.S1 and V.sub.S2 are sequentially A/D-converted and signal levels are read a plurality of times and they are added, and distance data L is calculated by a central processing unit (CPU) as follows. ##EQU1## where .alpha. is a constant.
In the above prior art, since the photo-currents I.sub.1 and I.sub.2 are sequentially processed, a ratio of the photo-currents I.sub.1 and I.sub.2 varies where a reflective index varies while a distance to an object such as a swinging curtain, does not change between the processings of I.sub.1 and I.sub.2. This creates an error in the distance data L.